Data collection in large-scale networks, in which specified low power radio is used, such as telemetering and monitoring in a large factory is examined. In these networks, PHY (physical layer)/MAC (Medium Access Control) standardized by IEEE (The Institute of Electrical and Electronics Engineers) 802.15.4 is used. Data is collected from a wide range and a large number of terminals by multihop. In a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) system, which is a radio access system standardized by IEEE802.15.4, respective terminals perform standby for a back-off time and carrier sense of a radio channel prior to packet transmission. When the terminals confirm with the carrier sense that the channel is in use (channel busy), the terminals perform the standby for the back-off time again (see Non Patent Literature 1).
On the other hand, there is proposed an access system for applying a centralized control-type access system and an autonomous distributed control-type access system in a time division manner for each of radio stations and each of radio channels (see, for example, Patent Literature 1). In the access system, when the radio station functions as a master station, the radio station transmits a signal according to control by the own station. When the radio station functions as a slave station, the radio station transmits a signal according to control by a master station. The radio station communicates with the other radio stations directly or via the other one or more radio stations. Consequently, the access system realizes guarantee of a low delay, low delay fluctuation, high throughput, and high QoS.
As another system for performing the time division control, there is proposed a media access control system for forming an upstream with a contention period and a contention-free period in a system including a base station, a relay station, and a subscriber station (see, for example, Patent Literature 2). In the media access control system, data is transmitted from the subscriber station to the relay station in the contention period. Data is transmitted from the relay station to the base station in the contention-free period. This enables communication between the subscriber station and the base station via the relay station.